This invention relates to a distributing valve for viscous materials, particularly twin cylinder pumps supplying concrete, said valve having a shaft in a casting which can be acted upon at least partially by the pump pressure, for moving an oscillating body with locking elements, which open a suction orifice for one pump cylinder and a pressure orifice for the other pump cylinder in one position of the oscillating body and are arranged to close the pressure orifice of the sucking cylinder and the suction orifice of the compressing cylinder. Such a valve will hereinafter be referred to as a valve of the type specified.
In concrete pumps the casing is usually arranged below a preliminary feed receptacle, into which the concrete is introduced, for example, by means of a conveyor mixer. One of the pistons of the pump sucks the concrete out of the preliminary feed receptacle into the appropriate cylinder, while the other piston forces the concrete sucked in during the previous stroke out of the other cylinder into a pipe. In general the casing has two pushing orifices arranged adjacent one another for the attachment of a Y pipe, to the other end of which a conveyor pipe for conveying the concrete is attached.
However the construction of the distributing valve should be such that in each position of the oscillating body, one cylinder has its suction orifice open and its pressure orifice closed while the reverse is true for the corresponding orifices of the other cylinder.
In a known distributing valve of the type specified, this requirement is fulfilled by arranging for the axis of rotation of the shaft to be roughly in the middle of the casing and by arranging that, in one of the two control positions, which are on diametrically opposite sides of the axis of the shaft, the suction orifice of one pump cylinder and the pressure orifice of the other pump cylinder are closed while the pressure orifice of the one and the suction orifice of the other pump cylinder are simultaneously open. In the other control position the functions are reversed. The disadvantage of this known method of construction lies in the problems of sealing and the problems of the resulting wear on the rotating shaft, which must lie within the part of the casing which is under pressure.